Biological samples may be preserved by cryogenic freezing. The biological samples are usually stored in disposable containers (disposables). The type of disposable container used depends on the type of sample. Examples of commonly used disposable containers include vials, straws and bags. The disposable container is stored at low temperatures in a Dewar flask typically filled with liquid nitrogen at a temperature of −196° C.
Vials are generally tubular in shape, with a tubular wall defining a main longitudinal cavity (the sample cavity) for storage of the sample. The sample cavity can be sealed by a lid. Freestanding cryogenic vials include a base portion below the sample cavity which enables the vial to stand upright without the need for a support rack. The base portion of a freestanding vial is usually tubular in shape with a width that may be less than or equal to that of the sample cavity.
Conventional freestanding cryogenic vials have tubular base portions of a specific size and shape chosen by the vial manufacturer. A given laboratory will generally purchase vials from a particular manufacturer. Other laboratory equipment for storing, moving, filling and examining the vials will be chosen to be compatible with the specific size and shape of vial used in that laboratory. The tubular base portion of a conventional freestanding vial typically has a smooth cylindrical inner wall which extends around the entire circumference of the base portion. The tubular base portion generally has a circular cross section in the transverse direction.
Stored biological samples can be identified by writing on the disposable containers themselves or by writing on labels which are then attached to the containers. These labels may be handwritten or printed and can include bar codes.
The methods of identification described above have the disadvantage that written notes on containers can easily be erased or smudged and labels containing handwritten notes and printed text or barcode information can fall off the disposable containers while they are stored inside the Dewar leading to unidentifiable samples. These problems are exacerbated by the cold conditions in which biological samples must be kept.
When performing an audit of biological samples stored in cold storage (at temperatures of −196° C.), the biological samples should not be allowed to warm up to a temperature greater than −130° C. It is therefore desirable to minimise the amount of time that a sample spends outside of the Dewar wherever possible.
Recording, monitoring and auditing of samples in cold storage takes a considerable amount of time and effort, even when samples are labelled using barcodes. An additional and undesirable increase in the time taken to record or audit samples arises as a result of frost which forms on the surfaces of disposable containers and their labels when they are removed from liquid nitrogen into relatively warmer temperatures. It is common for samples to be stored for many years (e.g. 15 years) but even after just one year in storage, the layer of frost which builds up on a disposable container can make it impossible to make an optical reading of a bar code on a label using a bar code reader because a layer of frost will block or diffract the light of the bar code reader. The container cannot be warmed up to remove frost as this would lead to destruction of the sample.
The frost can be wiped off the disposable container but this contributes to an undesirable increase in the amount of time taken to read the sample.
It is known that Radio Frequency ID (RFID) tags can be used to monitor a plurality of disposable containers stored at low temperatures of down to −196° C.
An RFID reader can be used to transmit an encoded radio signal to an RFID tag in order to interrogate it. Upon receiving the interrogation signal, the RFID tag transmits its identification information to the reader. This identification information may be a unique serial number assigned to a particular patient or to a particular sample.
In Europe and other countries outside of the US, RFID components for medical storage operate at an approved frequency of 13.56 MHz. It is important that the frequency used for the RFID tag does not lead to any undesirable interference with other electronic medical equipment. Lower medically approved frequency bands such as 125 KHz do not provide enough signal bandwidth to provide the tag with a useful user defined memory.
It is known that RFID tags may be attached to cryogenic vials in order to identify samples contained in the vials. US 2011/0199187 discloses RFID tags fixed to conventional freestanding vials using a tag/spring assembly as well RFID tags fixed to specially adapted vials. The bases of the specially adapted vials include features such as clips, tabs, bevelled edges, guides and stops required to locate and retain the RFID tag inside the base of the freestanding vial.
For the attachment of RFID tags to conventional freestanding vials, the tag/spring assembly must be fixed to the vial before the RFID tag can be fixed to the vial. This extra step adds undesirable time to the process of tagging the vials. In addition, the introduction of an extra component increases the risk that a component will fail resulting in the RFID tag falling out of the vial. For example, an assembly of separate parts clipped together and subjected to cryogenic temperatures of −196° C. can lead to stress failure.
The specially adapted vials are expensive to produce. Furthermore, in order to tag a sample which is already stored in a freestanding cryogenic vial under cryogenic conditions, the sample must be transferred from the conventional vial to the specially adapted vial. Transfer of the sample is impractical as it would involve warming the biological sample up to a liquid state which is undesirable.